The present invention concerns a hydraulic dashpot.
Hydraulic dashpots are preferably employed in motor vehicles to attenuate the motion of wheel suspensions attached by way of springs.
The dashpot includes a cylinder and a piston. The cylinder is full of shock absorbing fluid and divided into two compartments. The motion is attenuated by forcing fluid from one compartment into the other through preferably spring loaded ports in the piston.
A known method of attaining well defined decreased attenuation at low piston speeds is to provide bypasses hydraulically paralleling the ports in the piston and hydraulically connecting the two compartments. Providing the bypasses with variable cross-sections is also known.
European Patent 1 006 292 A1 discloses a dashpot of this genus. The bypass between the compartments is accommodated in an axial bore in the piston rod and provided with lateral outlets through the rod that communicate with each compartment. The piston is hollow and accommodates a rod that adjusts the bypass cross-section. The rod governs controls in the form of a needle valve. There is a drawback to this embodiment in that only a fixed bypass cross section can be attained. Thus, the fluid must flow through the same cross section during the compression phase as it does during the suction phase.
Blocking the bypass to fluid flowing either in one direction during the compression phase or in the other during the suction phase is known, but there is a drawback to this approach in that the flow can be regulated in only one direction.
The object of the present invention is to eliminate these drawbacks.
The advantages attained by the present invention derive in particular from the simplicity with which a bypass cross-section can be established for each direction of flow independently.